Heat shock protein 90 (Hsp90) is an essential evolutionarily conserved molecular chaperone in eukaryotes. Cancer cells rely on Hsp90 to chaperone activated oncoproteins, and its involvement in numerous signaling pathways makes it an attractive target for drug development. Surprisingly, however, the impact of Hsp90 inhibitors on cancer cells is most commonly cytostatic, and efforts to enhance the anti-tumor activity of Hsp90 inhibitors in the clinic remain a significant challenge. In this study, we show that dual inhibition of Wee1 tyrosine kinase and Hsp90 causes prostate cancer cells to undergo apoptosis. Gene-expression profiling revealed that induction of the intrinsic apoptotic pathway by this drug combination coincided with transcriptional down-regulation of Survivin and Wee1, an outcome not seen in cells treated separately with either agent. At the translational level, expression of these two proteins as well as activated Akt was completely abrogated. Similar results were obtained in prostate cancer xenografts. These data establish a novel therapeutic strategy to enhance the efficacy of Hsp90 inhibitors in prostate cancer, and they provide a mechanistic rationale for stimulating the pro-apoptotic activity of Hsp90 inhibitors.